Electron pulser for an x-ray tube to produce a pulsed beam of x-rays



A. J. GALE April 13, 1965 ELECTRON PULSER FOR AN X-RAY TUBE TO PRODUCE A PULSED BEAM 0F X-RAYS Filed March 3. 1961 ro H/GH 4 VOL TA @E TERM/NAL United States Patent Of" 3,178,578 ELECTRON PULSER EUR AN X-RAY TUBE T PRODUCE A PULSED BEAM 0F X-RAYS Alfred J. Gale, Lexington, ll/lass., assigner to High Voltage Engineering Corporation, Burlington, Mass., a corporation of Massachusetts Filed Mar. 3, 1961, Ser. No. 93,169 1 Claim. (Cl. 250-99) This invention relates to the acceleration of electrons to high energy and in particular to novel means tor providing pulsed operation of such an electron accelerator. One use of such an accelerator is in X-ray machines for radiography wherein it is desired to take a series of closely spaced pictures by pulsing the electron beam in the radiographic machine. The X-ray production is consequently also pulsed, so that a series of discrete timespaced exposures can be made upon a lilm.

My invention comprehends an electron accelerator for series pulsed operation comprising a voltage generator,

an acceleration tube, a source of electrons, means for deecting the electron beam across an aperture at the entrance or low velocity end of the acceleration tube in a controlled manner such that the frequency of deflection determines interval between pulses and the amplitude of deflection, entrance aperture and beam diameter in combination determine the duration of the individual pulses and further gating" the deflection electrical or magnetic eld in such a manner that a limited number of pulses are produced.

The invention may best be understood from the following detailed description thereof having reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic view of an X-ray machine for radiography;

FIG. 2 is an enlarged View of the entrance or low velocity end of the acceleration tube used in the device shown in FIG. 1.

Referring to the drawing and first to FIG. 1 thereof, the X-ray generator 1 therein shown comprises, broadly speaking, an electrostatic voltage generator 2 (of the type disclosed in an article entitled Electrostatic Generators for the Acceleration of Charged Particles by Van de Graaff, Trump and Buechner in Reports on Progress in Physics, vol. Xl, p. 1, 1948, and in U.S. Patents Nos. 1,991,236 and 2,252,668) and an evacuated acceleration tube 3 of the type disclosed in U.S. Patent No. 2,517,260. However, the invention is not limited to any particular type of voltage generator or acceleration tube and an electrostatic voltage generator 2 is shown in FIG. l merely by way of example. Regardless of the particular source of DC. (or A.C.) voltage, electrons produced at a cathode 4, which may comprise a suitable iilament, are accelerated in the evacuated acceleration tube 3 by means of the voltage which is produced across the extremities of the acceleration tube 3 by the voltage generator 2 in accordance with well-known principles. In accordance with the invention after initial acceleration of electrons emitted from the filament 4 or other electron source to moderate velocities, the electron beam from the filament 4 or other electron source is deflected across an aperture 5 in an apertured electrode 6 at the low voltage end of the acceleration tube 3 which electrode 6 serves effectively to block the passage of the electron beam except when the beam is directed towards the aperture 5. One representative circuit for accomplishing this objective is shown in FIG. 2. Referring thereto, the cathode 4 is connected electrically to the high (negative) voltage terminal 7 of the electrostatic generator 2, and a cathode cup 8, which acts like the conventional grid in a conventional triode is connected to an appropriate grid bias voltage source 9 through an appropriate gating circuit 16. The gating aussi/s Patented Apr. 13, 1965 circuit itl is optional Vand may be eliminated. However, in general, in thenradiographic applications with which the invention isprimarily concerned it will be desired to operate the X-ray generator so that itk gives groups vof pulses. The purpose of the gating circuit 19 is to bias the grid or cathode cup 8 beyond cutoff during the time interval between pulse groups, while permitting the passage of electrons from the cathode 4 during the time interval of pulsed operation.

Although either electric or magnetic detiecting fields may be employed, or indeed even a mechanical deflection means might be employed, in HG. 2 there is shown a pair of deliecting plates 11 between which a varying electric field is produced by a suitable detlecting voltage source 1?.. Any particular waveform of the deflecting field may be employed but in general the simplest waveform is the sinusoidal type. ln order that the electron beam from the cathode 4 may be focused at the aperture 5 in the apertured electrode 6 when the electron beam crosses this aperture 5, an einzel lens may be provided as shown in FIG. 2 for focusing purposes. This einzel lens comprises three cylindrical electrodes of which the central electrode 13 is connected to the cathode 4 whilst the other two electrodes 14, 1S are connected to the apertured electrode 6 which in turn is biased positively with respect to the cathode 4 by the extraction voltage source 16.

The electron beam is deflected across the aperture 5, so that the frequency of deflection determines the pulse repetition rate or interval between the beginnings of pulses. The duration of the pulse is determined by the size of the cross section of the beam, the size of the entrance aperture 5 and the speed with which the beam crosses the aperture 5. Assuming a given frequency and waveform, it is apparent that the velocity of movement of the beam is dependent upon the amplitude of deflection.

It will be noted that the electrons which impinge on the apertured electrode 6 are low Velocity electrons, so that there is no undue heating.

The pulsed beam so generated is then utilized in the conventional manner by acceleration through the uniform electrostatic field established by glass rings 20 and metal electrode rings 18, and by the impinging thereof upon X-ray producing target electrode 19 in accordance with the teachings of the above cited U.S. Patent No. 2,517,260.

Having thus described the principles of the invention, together with an illustrative embodiment thereof, it is to be understood that although specific terms are employed, they are used in a generic and descriptive sense and not for purposes of limitation, the scope of the invention being set forth in the following claim.

I claim:

An X-ray device adapted to take a series of closely spaced pictures consisting of an electron accelerator for series pulsed operation having (a) an electron emitting cathode,

(b) an X-ray producing target electrode,

(c) means for producing along said accelerator a uniform electrostatic field,

(d) a grid electrode proximate to said cathode,

(e) means for focusing into a beam electrons emitted from said cathode,

(f) an apertured electrode disposed proximate to said cathode and in transverse relationship to the electron beam emanating therefrom, said apertured electrode being positioned relative to said cathode and said X-ray producing target electrode so as to intercept the low energy portion of said electron beam, and

(g) beam deecting plates disposed between said cathode and said apertured electrode,

a gating circuit adapted to intermittently bias said grid electrode beyond cutoff, and means for activating said beam deecting plates in Such a marmer as to periodically 2,823,319 2/53 Vossberg Z50- 102 deect said electron beam across said apertured electrode 2,853,623 9/ 58 Kerns Z50-93 X and the aperture therein. 3,087,057 4/ 63 Gutter 315-30 X OTHER REFERENCES Electron Velocity Micro-Analyzer, by Rabah Shahbender, from RCA Technical Notes, RCA TN No. 310,

Bachman November Sheets). 2,517,260 8/50 Van de Graaic et al. 250--93 X 2,563,573 8/51 Baker 313--55 X RALPH NILSON, Primary Examiner.

References Cited by the Examiner UNITED STATES PATENTS 

